1. Field of the Invention
The present invention relates to a linear motor, a stage apparatus having the linear motor, an exposure apparatus having the stage apparatus, and a method for manufacturing a device using the exposure apparatus.
2. Description of the Related Art
A semiconductor exposure apparatus used to manufacture, for example, a semiconductor device or a liquid crystal display (LCD) device includes a stage apparatus (a wafer stage and a reticle stage) for moving and positioning a wafer and a reticle at a high speed. As a method for driving the stage, a linear motor using Lorentz force is commonly used. Since the linear motor is used, a stage mover unit can be driven at a high speed in a non-contact state with respect to a stator unit, and positioning can be performed with high accuracy.
Recently, for improving the productivity (throughput) of the semiconductor exposure apparatus, stage acceleration is to be further increased. As a reticle or a substrate is increased in size, a mass of a stage is also increased. Therefore, driving force defined as “a mass of a movable body” X “acceleration” is greatly increased, and as a large electric current is applied to a linear motor coil for stage driving, the heat generation amount is increased.
If generated heat of the linear motor is leaked to an ambient space, a measurement error occurs caused by a temperature variation of a space of an optical axis of a laser interferometer, which is a position measurement sensor of a stage, or a measurement error occurs caused by thermal deformation of an optical component such as a reflective mirror disposed in an ambient space. Further, a structure or a lens around the linear motor is thermally deformed, thereby deteriorating the exposure transfer accuracy.
Japanese Patent No. 4088728 discusses a configuration in which a coil is housed in a vacuum chamber and generated heat of a coil is inhibited by vacuum thermal insulation from being leaked to an ambient space. A configuration in which a coolant flow passage is formed on a surface of the coil at a magnet side, and part of the heat amount leaked to an ambient space (magnet side) among entire heat amount generated when electric current is applied to the coil is collected by a coolant (see FIG. 11) is discussed.
Japanese Patent Application Laid-Open No. 10-323012 discusses a configuration in which a thermal insulation material is disposed between a coil of a linear motor and a permanent magnet (see FIG. 12). Heat generated when an electric current is applied to the coil is inhibited by the thermal insulation material from being leaked to an ambient space (a magnet side).
However, the configuration of vacuum thermal insulation discussed in Japanese Patent No. 4088728 uses a space for ensuring a thickness of a vacuum area, a thickness of a vacuum chamber cover, which can endure differential pressure between a vacuum and an atmospheric pressure, and a thickness of the vacuum area against deformation of the cover by differential pressure. Therefore, a large gap has to be ensured between the coil and the magnet.
In a configuration in which a coolant flow passage 99 is formed as illustrated in FIG. 11, most of the heat of the coil comes into a coolant of the coolant flow passage 99 through a thin sheet 82 disposed in contact with the coil 38. Since the heat amount that comes into the coolant is large, an appropriate coolant flow rate is used, so that a large space for the coolant flow passage 99 is also used.
Further, a cover thickness for preventing a cover 36 from being damaged by the coolant pressure and a space for accepting pressure deformation of the cover are used. Therefore, this configuration also uses a large gap between the coil and the magnet.
Therefore, in the configuration of Japanese Patent No. 4088728, since the gap (so-called magnet gap) between the coil and the magnet is large, the efficiency of the linear motor deteriorates. As a result, an electric current for generating sufficient trust force is increased, thereby increasing heat generation.
In the configuration of Japanese Patent Application Laid-Open No. 10-323012, as a value d/λ (herein referred to as “thermal resistivity R”) obtained by dividing a thickness d (a unit is m) of the thermal insulation material by a thermal conductivity λ (a unit is W/mk) is increased, the heat amount leaked to the ambient space is decreased. In other words, as the thermal conductivity λ is decreased and the thickness d is increased, the heat amount leaked to the ambient space can be suppressed as much.
However, if the thickness of the thermal insulation material is large, the magnet gap is increased, so that the efficiency of the linear motor is lowered. As a result, the heat generation amount is increased.
It is beneficial to select a thermal insulation material with small thermal conductivity, to reduce the thickness of the thermal insulation material. However, the thermal conductivity of the thermal insulation material has a limit. Generally, a commercially available thermal insulation material (for example, rigid urethane) is 10−2 in thermal conductivity (a unit is W/mK), and a vacuum thermal insulation material (the inside of a packaging material vacuum to lower a thermal conductivity) is 10−3 in thermal conductivity.
If a thermal resistivity R0 used to make the leakage heat amount equal to or less than a certain value, even though a thermal insulation material with a minimum available thermal conductivity λmin is used, a thickness dmin (=R0×λmin) is to be used. A configuration of only the thermal insulation material is difficult to obtain a higher effect of suppressing the leakage heat amount at a thickness equal to or less than dmin. That is, a thickness of the thermal insulation material is determined by an available thermal conductivity of the thermal insulation material. Therefore, it is difficult to make the thickness of the thermal insulation material thin while suppressing the leakage heat amount.